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Fractions owing to the heterogeneous degradation of the wood pulp constituents
Across the cell wall layers. Intrinsic strength properties from a polymeric
Material are always related to the weakest part in the polymer, which is represented
By the short-chain molecules. A detailed evaluation of the numerical data from
GPC measurement revealed that zero-span tensile strength correlates well with
the weight percent of the DP <120 fraction, as illustrated in Fig. 11.4.
The intrinsic viscosity as well as standard information from GPC measurements
Such as PDI or DPw and DPn are not suited to predict the fiber strength
Properties accurately. However, the amount of low molecular-weight fraction comprising
The DP range between 100 and 150 is a suitable measure to estimate fiber
Strength properties, regardless of the origin of pulp (wood species, pulping,
Bleaching processes). This example clearly demonstrates that the macromolecular
Properties are a decisive element of strength characteristics of a pulp fiber. These
Results are in good agreement with the findings of Kettunen et al. that tearing
Strength of a pulp increased with increasing amounts of high molecular-weight
xylan [24].
However, sheet properties are determined by many other parameters such as
the cellulose:hemicellulose ratio, as previously discussed. Another important factor
For pulp sheet properties is fiber morphology, characterized by fiber length,
Fiber length distribution, and coarseness. It is widely accepted that especially
Pulp Properties and Applications
2 4 6 8
Zero-Span tensile index, dry [Nm/g]
Weight fraction < DP 120
Fig. 11.4 Relationship between zero-span tensile index and
the weight fraction <DP 120 of a representative selection of
Commercial hardwood and softwood kraft and sulfite pulps
[17]. For more detailed information on these pulps, see
Tabs. 11.1 and 11.2.
Tearing strength is influenced by fiber length. Based on the comparison between
Hardwood and softwood kraft pulps, the poorer tearing strength of the former is
Generally attributed to the shorter fiber length. The results of the measurement of
The fiber dimensions of the selected paper pulps are provided in Fig. 11.5 and
Tab. 11.3.
By comparing the fiber length distribution of both spruce pulps, it is apparent
That the sulfite pulp shows a higher proportion of short fibers as compared to the
Kraft pulp. This may be attributed to the degraded cellulose fraction formed during
The late stage of cooking. The beech pulp shows the characteristic peak at a
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Beech Sulfite Beech Kraft Eucalyptus Kraft | | | Fiber length below 0.2 mm, indicating the presence of large amounts of fines derived |